Re: [PATCH v10 3/9] s390x/cpu_topology: resetting the Topology-Change-Report

[Thomas Huth <thuth@xxxxxxxxxx>]

On 12/10/2022 18.21, Pierre Morel wrote:
> During a subsystem reset the Topology-Change-Report is cleared
> by the machine.
> Let's ask KVM to clear the Modified Topology Change Report (MTCR)
>   bit of the SCA in the case of a subsystem reset.
>
> Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
> Reviewed-by: Nico Boehr <nrb@xxxxxxxxxxxxx>
> Reviewed-by: Janis Schoetterl-Glausch <scgl@xxxxxxxxxxxxx>
> ---
>   target/s390x/cpu.h           |  1 +
>   target/s390x/kvm/kvm_s390x.h |  1 +
>   hw/s390x/cpu-topology.c      | 12 ++++++++++++
>   hw/s390x/s390-virtio-ccw.c   |  1 +
>   target/s390x/cpu-sysemu.c    |  7 +++++++
>   target/s390x/kvm/kvm.c       | 23 +++++++++++++++++++++++
>   6 files changed, 45 insertions(+)
>
> diff --git a/target/s390x/cpu.h b/target/s390x/cpu.h
> index d604aa9c78..9b35795ac8 100644
> --- a/target/s390x/cpu.h
> +++ b/target/s390x/cpu.h
> @@ -825,6 +825,7 @@ void s390_enable_css_support(S390CPU *cpu);
>   void s390_do_cpu_set_diag318(CPUState *cs, run_on_cpu_data arg);
>   int s390_assign_subch_ioeventfd(EventNotifier *notifier, uint32_t sch_id,
>                                   int vq, bool assign);
> +void s390_cpu_topology_reset(void);
>   #ifndef CONFIG_USER_ONLY
>   unsigned int s390_cpu_set_state(uint8_t cpu_state, S390CPU *cpu);
>   #else
> diff --git a/target/s390x/kvm/kvm_s390x.h b/target/s390x/kvm/kvm_s390x.h
> index aaae8570de..a13c8fb9a3 100644
> --- a/target/s390x/kvm/kvm_s390x.h
> +++ b/target/s390x/kvm/kvm_s390x.h
> @@ -46,5 +46,6 @@ void kvm_s390_crypto_reset(void);
>   void kvm_s390_restart_interrupt(S390CPU *cpu);
>   void kvm_s390_stop_interrupt(S390CPU *cpu);
>   void kvm_s390_set_diag318(CPUState *cs, uint64_t diag318_info);
> +int kvm_s390_topology_set_mtcr(uint64_t attr);
>   
>   #endif /* KVM_S390X_H */
> diff --git a/hw/s390x/cpu-topology.c b/hw/s390x/cpu-topology.c
> index c73cebfe6f..9f202621d0 100644
> --- a/hw/s390x/cpu-topology.c
> +++ b/hw/s390x/cpu-topology.c
> @@ -107,6 +107,17 @@ static void s390_topology_realize(DeviceState *dev, Error **errp)
>       qemu_mutex_init(&topo->topo_mutex);
>   }
>   
> +/**
> + * s390_topology_reset:
> + * @dev: the device
> + *
> + * Calls the sysemu topology reset
> + */
> +static void s390_topology_reset(DeviceState *dev)
> +{
> +    s390_cpu_topology_reset();
> +}
> +
>   /**
>    * topology_class_init:
>    * @oc: Object class
> @@ -120,6 +131,7 @@ static void topology_class_init(ObjectClass *oc, void *data)
>   
>       dc->realize = s390_topology_realize;
>       set_bit(DEVICE_CATEGORY_MISC, dc->categories);
> +    dc->reset = s390_topology_reset;
>   }
>   
>   static const TypeInfo cpu_topology_info = {
> diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
> index aa99a62e42..362378454a 100644
> --- a/hw/s390x/s390-virtio-ccw.c
> +++ b/hw/s390x/s390-virtio-ccw.c
> @@ -113,6 +113,7 @@ static const char *const reset_dev_types[] = {
>       "s390-flic",
>       "diag288",
>       TYPE_S390_PCI_HOST_BRIDGE,
> +    TYPE_S390_CPU_TOPOLOGY,
>   };
>   
>   static void subsystem_reset(void)
> diff --git a/target/s390x/cpu-sysemu.c b/target/s390x/cpu-sysemu.c
> index 948e4bd3e0..707c0b658c 100644
> --- a/target/s390x/cpu-sysemu.c
> +++ b/target/s390x/cpu-sysemu.c
> @@ -306,3 +306,10 @@ void s390_do_cpu_set_diag318(CPUState *cs, run_on_cpu_data arg)
>           kvm_s390_set_diag318(cs, arg.host_ulong);
>       }
>   }
> +
> +void s390_cpu_topology_reset(void)
> +{
> +    if (kvm_enabled()) {
> +        kvm_s390_topology_set_mtcr(0);
> +    }
> +}
> diff --git a/target/s390x/kvm/kvm.c b/target/s390x/kvm/kvm.c
> index f96630440b..9c994d27d5 100644
> --- a/target/s390x/kvm/kvm.c
> +++ b/target/s390x/kvm/kvm.c
> @@ -2585,3 +2585,26 @@ int kvm_s390_get_zpci_op(void)
>   {
>       return cap_zpci_op;
>   }
> +
> +int kvm_s390_topology_set_mtcr(uint64_t attr)
> +{
> +    struct kvm_device_attr attribute = {
> +        .group = KVM_S390_VM_CPU_TOPOLOGY,
> +        .attr  = attr,
> +    };
> +    int ret;
> +
> +    if (!s390_has_feat(S390_FEAT_CONFIGURATION_TOPOLOGY)) {
> +        return -EFAULT;

EFAULT is something that indicates a bad address (e.g. a segmentation fault) 
... so this definitely sounds like a bad choice for an error code here.

 Thomas